\begin{tikzpicture}
    \tkzDefPoints{0/0/B, 4/0/C, 4/3/A}
    \tkzDefMidPoint(A,C)  \tkzGetPoint{O}
    \tkzInterLC[common=A](B,A)(O,A)   \tkzGetFirstPoint{D}

    \tkzDrawPolygon(A,B,C)
    \tkzDrawCircle[thick](O,A)
    \tkzDrawPoint(O)
    \tkzLabelPoints[above](A)
    \tkzLabelPoints[left](B)
    \tkzLabelPoints[below](C)
    \tkzLabelPoints[above left](D)
    \tkzLabelPoints[right](O)
\end{tikzpicture}

